1. Field of the Invention
This invention pertains to the field of automatic transmission controls.
2. Description of the Prior Art
In an automatic transmission, when the operator moves the range selector lever from the neutral or park position to forward or reverse position, the proper friction element is engaged or applied to produce the selected operating range. This engagement must be accomplished in a smooth manner to prevent noise, vibration, and harshness. However, this engagement must occur rapidly so that the transmission is fully engaged when the operator depresses the engine throttle, in order to prevent a slip-bump distrubance.
In an automatic transmission, forward drive and reverse drive engagement occur when the vehicle operator moves the shift selector lever from the park or neutral positions to a forward drive range or reverse drive range position. Conventionally, the oncoming friction element, which produces the selected drive ratio when engaged, is stroked briefly to take up clearances in the friction element, whereafter clutch pressure is increased so that the oncoming friction element is fully engaged within a fixed period.
If the oncoming friction element pressure increases too quickly, then a harsh engagement can occur. If the oncoming friction element pressure increases too slowly, then the friction element may not be fully engaged when the vehicle operator depresses the engine throttle pedal, thereby producing a slip-bump disturbance.